[frontrange]

I really faked up. I had the knee lock set and forgot it. So today I started playing with peck drilling, and after quite a few pecks, the machine knee seized up. As soon as I realized what happened I loosened the lock and started dousing the Vee way above the lock with PB blaster, but its locked up tight as a drum.

I tried freeing the gib from the top but the slotted part of the gib was broken off. I also tried to loosen it from the bottom but it won't budge.

Gawd I feel sick. Even if I get it loose somehow the casting must be gouged now. Any ideas?

TIA

[HuFlungDung]

There have been several discussions about this over on practical machinist forums.

[frontrange]

After reading the post about complete disassembly and laying the column back to tap out the gib from underneath I was really feeling sick.

The story has a happy ending though, I just got the gib loose. I was thinking about jamming a rod under the gib, running the table back to the column, loosening the pedistal and raising it, then putting a bottle jack between the table and ram.

This morning when the factory opened I called Lagun and talked to a tech. He told me the way I planned was how they did it. Half hour later I had it done. No drama at all (at least till I got a quote on a replacement gib...) Whew!

[HuFlungDung]

Good for you!

[frontrange]

Thanks - I was really down this morning before talking to the Lagun tech. I'd just got a 4th axis installed as was really beginning to have fun with this machine till I broke it.

One thing is for sure, that knee lock handle is staying in a baggie from now on. I don't know why I didn't take it off long ago, I'm just too used to manual operation I guess. I can't believe those Servo motors can fast peck a locked knee. Funny I'd been thinking it would be nice to install some load meters on each axis. Guess I should get around to doing it now.

[thebodger@roger]

Yup,
Keep that lock in a baggie. Let the servos or stepper do the locking. I know the mechanical locks can improve stiffness, but they can also seize the gib, if the circumstance is provided.

[frontrange]

I just wish someone had told me that before I broke a $400 gib. An expensive and stressful lesson that will not soon be forgotten.

[machintek]

The only Bridgeport that used the knee was the old S2NC. And it had a air over oil quill feed for drilling to keep knee action to a minimum + a air assisted knee.
Typically there is also a automatic oiler that pumps a shot of oil about every 20 minutes or so to the knee. Does your machine have that? Is this a conversion?
When ordering a gib from Bridgeport, you received a raw gib unless you specified the size and paid for the scraping and oil grooves to be put in. just in case you need to know this.

George

[frontrange]

Actually its a Lagun FTV-2. I was told by the tech at Lagun that they only made a couple of machines with a ball screw under an air assisted knee and fitted with a Servo II system - I have one of them thanks to a lucky buy on Ebay.

And yes it has an auto lube system as well.

I was told the scraping needed would be minimal - I do know I need to do the oil groove and adjustment screw slot too.

[mactec54]

frontrange

You can repair the gib that came out & put a new piece on top, that is why it jamed up to start with, the piece that was missing off the top is what holds the gib in place,without it the gib will slide down & jam the knee, it was nothing to do with the knee being locked that made it jam, Just the gib missing it's retainer, with the peck drilling it was able to pull the gib down

[frontrange]

I know the retainer losing it's grip on the gib when the top broke off was when things went south, but of course that happened because the gib was locked during a fast peck operation in the first place.

How would you repair the gib?? I assumed this is cast iron as it is very brittle. I guess you could heat/braze and cool slowly but it hardly seems worthwhile since it could still have cracks that would get you back into the same problem all over again...

[mactec54]

frontrange
The knee on your machine was no designed to do peck drilling, just smooth up & down movements, There are a lot of different way's to repair the gib, one you can just mill a new slot in it for the ajusting screw & then you have to glue a shim on the back of the gib, the whole of the back needs to have the shim on & shaped the same as what the gib is, If you went with welding it you would have to bronze weld it, stick weld it you could get cracking as you said, you could mill a flat on the back of the gib & attach a stepped steel plate/block & screw/bronze this in place it won't crack if you braze it properly

[frontrange]

The shim is a good idea, I wish I had thought of that before ordering another gib. I may give them a call Monday morning and see if it's gone out yet.

[79TigerPilot]

Boy, is this some good informaiton. I just got my BP J head knee drive working yesterday. I will have to remove the knee lock just to be sure it doesn't get locked and rip the the top of the gib off. I am always worried when I remove the gib that it could get away from me and drop down and jam things up.

Anyone got a good procedure for how to set up the knee gib adjusting screw?

Craig

[SCzEngrgGroup]

Boy, is this some good informaiton. I just got my BP J head knee drive working yesterday. I will have to remove the knee lock just to be sure it doesn't get locked and rip the the top of the gib off. I am always worried when I remove the gib that it could get away from me and drop down and jam things up.

Anyone got a good procedure for how to set up the knee gib adjusting screw?

Craig

Craig,

I set all my gibs based on backlash measurement. Lube the ways well, then run it up and down, and measure the backlash. Start loose, and keep tightening in 1/4 turn increments until you see backlash jump up, then back off 1/4-1/2 turn.

Regards,
Ray L.

[frontrange]

Mactec54 - The more I think about your shim fix the more I wish I'd thought of that myself - simple and elegant solutions are the best kind...

I'm going to go ahead and give it a shot while I'm waiting for the new gib assuming it's already in transit. How do you recommend fixing the shim to the non-bearing surface of the gib? I was thinking maybe drill a couple of holes in the shim stock after cutting it to size and soldering it with dabs of silver solder in the holes, but you referred to gluing it? Could you elaborate please? I assume I will still have to re-scrape the bearing surface once it's shimmed?

I also liked your idea on making a stepped block to fit the broken off end, but since this is my only milling machine and it's broke- making more precision parts is, uh , problematic.

I also have to agree with you on the peck drilling using the knee. I envisioned that happening a lot slower that it did once the machine was executing the code. That knee was moving really fast. It was kind of breathtaking before it all went south...

frontrange
The knee on your machine was no designed to do peck drilling, just smooth up & down movements, There are a lot of different way's to repair the gib, one you can just mill a new slot in it for the ajusting screw & then you have to glue a shim on the back of the gib, the whole of the back needs to have the shim on & shaped the same as what the gib is, If you went with welding it you would have to bronze weld it, stick weld it you could get cracking as you said, you could mill a flat on the back of the gib & attach a stepped steel plate/block & screw/bronze this in place it won't crack if you braze it properly

[79TigerPilot]

When I had my table and ways ground and scraped they had to shim the gibs because of the material removed from the ways. They epoxy bond on what I think was Turcite-B Slydway or similar high performance thermoplastic to the sliding side of the gib. After bonding they ground and scraped it to the proper taper fit.

http://www.aetnaplastics.com/Product...astics/Turcite

Craig

[mactec54]

frontrange
You can glue it with any good epoxy glue, clamp it down so it is niece & flat, I would not try to silversolder the shim on,even superglue will hold it on,

79TigerPilot What they did with your gibs is put the turcite on the front of the gib, this works good if you have way covers, if you don't have way covers the first chip that gets in there will rip the Turcite away, when rebuilders put it on the back of the gib they mostly use strips of Phenolic or steel shim, Glued to the gib the same way, when you use a steel shim & get the right thickness & the gib is straight not further work is needed on the gib

If you want to set the Gib to how it should be done, you ajust it to have .0005 of backlash

[frontrange]

mactec54 - How do you measure that backlash? Is that from side to side by rocking the table?

[mactec54]

frontrange

Yes thats one way, Mount your indicator on the side of the knee up near the top & then near the bottom, check it with the knee in different places as you may have wear on the column